I have purchased and built up a couple of power amp pcbs, they require + and - 50v rails.

I have a large toroidal transformer with 2 40v secondaries and 2 25amp bridge rectifiers, I know how to put together an unregulated supply but want it regulated, anyone know of a good cct or a link to somewhere I can read about regulation.

I seem to remember 2N3055 and it's compliment were good for hi current circuits.

40 VAC will give you roughly 54-55 V raw DC, if you want regulated supplies from that voltage, the voltage differential won't be enough for 50v regulated. For that (depending on the type of the regulator's dropout voltage), you need at least 8-10 volts difference between the input and output. Less with BJT types, more with FET-s.
Anyway, if you want to use them for power amp stages, you don't really need regulated supplies, specially with symmetrical supply ones, since their common mode PSRR (ripple rejection ratio) is rather good, there -if you really want one- you can use a simple capacitance multiplier type filter. There the drop will be around 4-5 Volts (with Darlingtons -or connected as Darlington types).
Of course all above comments are valid for a power transformer, where the secondary voltages won't drop too much under heavy load conditions.....

He was thinking of using 3055's as pass transistors for the regulators. Voltage ok, but beta is too low. You'd need half a dozen in parallel and another to drive them. I'd be thinking MJ11015 and its complement (30A) or MJ11032 (50A).

If you just want to lower the voltage to +/-50V, add a couple of turns around the outside with some #14 soild core THHN and wire it in series with the PRIMARY. That is, make it a higher voltage primary. Check polarity and # of turns with a light bulb in series first. When the secondary output drops (and magnetization current drops too) you've got the polarity of the extra winding right. Spread the turns evenly around the core for best performance. Do not use magnet wire for this - use the insulated stuff -- it's safer.

I have purchased and built up a couple of power amp pcbs, they require + and - 50v rails.
I have a large toroidal transformer with 2 40v secondaries and 2 25amp bridge rectifiers, I know how to put together an unregulated supply but want it regulated, anyone know of a good cct or a link to somewhere I can read about regulation.

You don't have what it takes to regulate it down to +/-50V.

That said, you'll have raw +/- 56V or a little less, not ridiculously too much.

Post what amp you have, and specially its output transistors ... *maybe* it can work with +/- 56V

RMX1450 uses three C5200/1943 pairs and +/-67 V rails and they don't blow up often. Yours will be fine with 4R loads.

You don't overlook the voltage in the load, because in this mode of operation voltage is lower than those +/- 67Vdc (falls below +/-60Vdc). Under these conditions the voltage peak to peak on 4 Ohm load may be about ~100Vpp, which means ~35Vrms on the load; or otherwise, about 300W / 4 ohm.